FIG. 5 shows an example of a known hydraulic tensioner used in the timing drive system of an automobile engine or the like. The tensioner comprises a synthetic resin body 510, which can be attached to the side of an engine block, a metal cylinder 520 fitted into a circular hole 511 formed in the body 510, a plunger 540 inserted into the metal cylinder 520 in such a manner that the tip of the plunger 540 protrudes from the body 510, and a compression spring 530, inside the metal cylinder 520, for urging the plunger in the protruding direction so that the plunger presses the shoe of a tensioner lever (not shown) against a timing chain. A check valve mechanism 550, permits the flow of oil under pressure into an oil chamber formed between the inside of the plunger 540 and the metal cylinder 520, but blocks reverse flow. A blocking mechanism 560, comprising ratchet teeth 541 formed on an outer surface of the plunger 540, and a spring-biased pawl 561 engaged with the ratchet teeth 541, blocks retracting displacement of the plunger 540, which would otherwise occur when excessive impact force is exerted on the plunger by the timing chain upon starting of an engine. The tensioner shown in FIG. 5 is described in Japanese laid-open patent publication No. 2002-86104 at Page 6, left column, line 30 to page 6, right column, line 41.
In the above-described conventional hydraulic tensioner, the metal cylinder 520 is concentric with the circular hole 511. Consequently, in the assembly process, twisting of the metal cylinder is apt to occur as the cylinder is positioned in the hole 511. The ability of the metal cylinder to twist prevents rapid and accurate assembly of the tensioner. Moreover, twisting of the metal cylinder can prevent proper engagement of the ratchet pawl 561 with the ratchet teeth 541 on the plunger, preventing reliable application of tension to the transmission medium, causing vibration and noise due to reverse movement of the plunger, and potentially causing damage to the entire timing drive system.
Rotation of the metal cylinder 520 can also occur as a result of torsion applied by the compression spring 530 during operation of the tensioner, with the same adverse effects, namely, failure of the pawl to engage the ratchet teeth properly, unreliable application of tension, generation of noise, and damage.
The tendency of the metal cylinder to twist in the tensioner body can be avoided by measures such as welding, or the use of an adhesive, to fix the metal cylinder in the tensioner body. However, these measures are time-consuming and make assembly of the tensioner difficult.
Objects of the invention, therefore, are to solve the above-described problems encountered in conventional hydraulic tensioners; to provide a hydraulic tensioner that suppresses the vibration noise and breakage which are apt to occur during operation; and to achieve a hydraulic tensioner that can operate reliably over a long period of time. It is also an object of the invention to provide a versatile tensioner construction, in which selective assembly of any of various inner tensioner bodies with an outer body can be carried out efficiently, in order to accommodate various different forms of tensioner mounts.